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Working of oscillator-with Quartz crystal

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pthoppay

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working of oscillator

Hi all,

I have attached a colpitt oscillator, which has quartz crystal in the feedback. When i tested the circuit without the crystal it is operating at the required frequency, but when I insert the crystal in the feedback loop it is oscillating.

I would like to know, what might be the possible resons behind this, please help me on this.

Regards,
Prakash.
 

bjeservice

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working of oscillator

did you mean when you puts the crystal it does not oscillating
 

pthoppay

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working of a oscillator

yes, when I put the crystal in the feedback path it is not oscillating.

Prakash.
 

qslazio

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working of an oscillator

Can anyone tell me the function of inductor L10?
thanks
 

pthoppay

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working of oscillator

Hi,

It is used for pulling the resonant frequency of the oscillator.

Prakash.
 

Teddy

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Are you sure you are not overdriving the xtal?
 

VSMVDD

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crystals above 30mhz mostly run in overtone mode

keep this in mind

134mhz direct frequency is hard to achieve from a thin sliver of quartz

maybe reduce the xtal to a sub harmonic
and run in overtone mode is best and most stable

appart form this the transistor needs a load resistor added

or as pointed out youll overdrive it

? what supply voltage are you using ??? 5v dc ??

did you measure dc bias and check its right ???

should be ~ .707v base-emiter

r12 emiter side {between the choke coil and r12
should also have a decoupling cap added to gnd

or the resistor may act as a spring instead and dampen the oscilation}
adding an electrolytic 1uf @10v or 10nf ceramic will help here

and why does L10 have a 0R resistance ????

0R = 0 reactance also
 

pthoppay

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Hi,

Thanks for the reply.

I am using overtone crystal. I am using a 5th overtone crystal.

For the load resistor I am using 100k.

Supply voltage is 3V.

I removed the inductor in series with the crystal as I dont need to pull the crystal. Hence i named it 0R. I will try using capacitor in parallel with the emitter resistor.

Meanwhile, I didnt undertsand the overdrive concept, can anyone expalin in detail about this concept.

Prakash.
 

E-design

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At this frequency you will need about 200-300nH across the crystal terminals to resonate out the 5-7pF of holder capacitance for the crystal to operate as it should. Just make sure the inductor has a SRF higher than the frequency you want to use.
 

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